Large integrated circuit power devices are commonly used to provide large amounts of current to drive external loads. These devices can provide on the order of one-half amp to ten amps or higher and are commonly formed using large lateral or vertical MOS structures. A chief concern in circuits used to drive external loads is monitoring the current provided by the integrated power device. Conventional methods of sensing this current place a small resistor in series with the power device and measure the voltage drop across the resistor to determine the current output by the power device. This approach suffers from the problem that the resistor dissipates a great deal of power due to the high current levels passing through it and voltage drops across this resistor reduces gate drive resulting in an increase in the output resistance of the power transistor.
A more sophisticated approach to monitoring the output current involves the use of a sense device constructed and connected in parallel with the power device. The sense device is commonly a second MOS device which is constructed using the same processes as the power device but which is many hundreds times smaller than the power device. The sense device drives a current that is proportional to the current passing through the power device. As such, the sense device can be used to track and control the amount of current output by the power device. In order to accurately track the amount of current output by the power device, the sense device must be constructed proximate the power device. The power device commonly occupies a great deal of the surface of the semiconductor substrate. If the sense devices are put on the periphery of the area occupied by the power device, the sense device may not accurately track the operation of the power device due to thermal gradients present within the integrated device.
Accordingly, a need has arisen for a method of constructing an integrated device comprising a sense and a power device that reduces or eliminates disadvantages associated with prior configurations.